Production of monofilaments obtained from highly viscous alpha-olefin polymers



June 11, 1963 E. BARATTI PRODUCTION oF MoN EQEUEQSE E Ezio INVENTOR.

ENRlCO BARATTI ATTORNEY United States Patent O 3,092,891 PRODUCTION OFMONOFILAMENTS OBTAINED FROM HIGHLY V I S C O U S ALPHA-OLEFIN POLYMERSEnrico Baratti, Milan, Italy, assignor to Montecatini Societa Generaleper llndustria Mineraria e Chimica, Milan, Italy Filed July 27, 1959,Ser. No. 829,519 Claims priority, application Italy Aug. 1, 1958 8Claims. (Cl. 28-82) The present invention relates to a process for theproduction of monofilaments derived from alpha-olefin polymers having ahigh intrinsic viscosity. More particularly, the invention is directedto monofilarnents derived from polypropylene and from a mixture ofpolypropylene and polystyrene.

Alpha-olefin polymers have been described in the lournal of PolymerScience, April 19, 1955, volume XIV, Issue No. 82, pages 143-54.Furthermore, a low pressure process for the stereospecificpolymerization of propylene and other higher alpha-olefins has beendescribed by Natta et al. in Italian Patent No. 526,101, issued November14, 1955.

In accordance with the preceding references, it has been establishedthat various types of fibers can be obtained from alpha-olen polymersand in particular from polypropylene. These fibers have excellentproperties for a wide variety of purposes, and were derived from apolymer having a medium intrinsic viscosity. On the other hand, polymershaving a very high viscosity and having high crystallinity althoughproduced by the foregoing polymerization processes have not heretoforebeen generally made into fibers due to various difficulties encounteredin fabrication processes, particularly in spinning and orienting.Particular poly alpha-olefins not generally amenable to liber-makingprocess are crystalline propylene polymers having a very high intrinsicviscosity (above 1.8), but these same polymers, if made into orientedbers should exhibit outstanding characteristics, such as high tenacity,high elasticity and low brittleness.

An object of the present invention is to obtain monofilaments fromalpha-olefin polymers of high intrinsic viscosity.

Another object of this invention is to provide a process for theproduction of monolaments derived from alphaolefin polymershaving a highintrinsic viscosity.

Another object is to provide monofilaments made of a highly viscousmixture of polypropylene and polystyrene, said monofilaments beingespecially suitable for brooms and the like.

Other objects and advantages of this invention will become apparent uponfurther study of the specification and the appended claims.

It has, in fact, been ,surprisingly found that, if the monofilamentsobtained by extruding propylene polymers or mixtures based mainly onpolypropylene are subjected to specific multi-stage stretchingtreatments, fibers or filaments having excellent properties can beobtained.

According to this invention, a monofilamentabtained by extrusion ofpolypropylene with an intrinsic viscosity higher than 1.5 or of amixture based mainlyon polypropylene is subjected to a first quenchingtreatment and then to a multiple stretching in three stages, the entirestretching ratio being between 7:1 and 8:1. The steps must be carriedout in the following manner:

QUENCHING STEP Quick cooling of the monofilament can be obtained byplacing a quenching bath at a distance of about 10 cm. from thespinneret outlet. This quenching bath can be maintained at about C. inorder to obtain quick cooling. Obviously, this quenching step is a heattransfer 3,092,891 Patented June 11, 1963 ICC operation and othersystems yielding the same result can be employed. Such variables as thediameter of the filament, the speed of lament travel, the temperature ofthe bath, the ambient temperature, the cooling liquid, etc. can be usedto advantage by the designer.

FIRST STRETCHING STAGE This stage is conducted at room temperature. Thestretching ratio in the first stage is from 3:1 to 5: 1, and preferably3.8: 1.

SECOND STRETCHING STAGE This stage is conducted by immersing thefilament in a heat transfer medium such as water, so that the stretchingis conducted at approximately the boiling tmeperature of water orslightly lower than C. The stretching ratio is from 1.5:1 to 1.9:1, andpreferably 1.7:l.

THIRD ST RETCHING STAGE This stretching stage is conducted at roomtemperature. The stretching ratio is in the range of about 1.1:'1 to1.2: 1.

The process of the invention is shown diagrammatically in theaccompanying drawing.

If the monofilament must be wound on reels after the stretchingoperation, it is passed directly to the Winder. If, yto the contrary, itmust be used as brush bristles and must, therefore, be prepared in theform of pieces of various lengths, it is preferably subjected to afurther treatment. This is accomplished by allowing the treated filamentto stand for 24 hours, and it is then treated with steam at C. for about10 minutes in order to complete crystallization and to obtain a higherelasticity.

Only by the process of this invention is it possible to obtainpolypropylene filaments having an intrinsic viscosity higher than 1.5,preferably of about 2-2.2 or even higher and which exhibit tenacitieshigher than 6 g./den. It has been found that by processing filaments instrict accordance with the present invention, it is possible to producefilaments having about a 20% higher tenacity than those filamentsproduced by all other methods. A further outstanding property of thefilaments produced by this invention is that these same high tenacitiesare obtained with filaments having unusually high diameters in the rangeof from 0.30-0.40 mm. In contrast, it is established that with otherpolymers having even higher densities, such as nylon, much lowerdiameter filaments are required to yield tenacities in the range of 6g./den.

According to another embodiment of this invention, it has been foundthat mixtures of polypropylene and polystyrene, when subject to amultiple stretching in three stages, under the same above-describedconditions of ternperature and stretching, yield filaments having aneven higher hardness, a higher whiteness and a lower deformability thanthe corresponding unmodified polypropylene products. These filamentsalso exhibit high tensile strength and very high tenacity values and aretherefore eminently suitable as filaments for brushes and brooms. Forthis purpose, they have the further advantage to the fact that theyexhibit a lower deformability during their manufacture. And of evengreater importance, when they are subjected to strain during use theyreassume their original shape more promptly and with a higher release.The ratio of polypropylene to polystyrene is generally from 8:2 to9.8:0.2, preferably 9: 1.

Another advantage of the bristles of this invention is that feathering(unraveling the ends of each bristle into a small bundle of parallelfilaments) is facilitated. This feathering softens the point of eachbristle thus rendering it particularly suitable for the use in the broomfield.

The monofilaments and, therefore, the bristles obtained therefrom canhave a diameter of between 0.15 and 0.70 mm. Various samples ofmonofilaments obtained from 100% polypropylene and having a length of 98mm. and a diameter of between 0.24 and 0.340 mm. (diameters determinedin a Palmer micrometer) were tested in a motor dynamometer having acapacity of 5 to 15 kg. and a tensile rate of 50 cm. per minute, at 20C., with a relative humidity of 69%, and showed a tensile rin the rangeof 3.7-3.8 kg. and an elongation at break of 21- 22%. In a similarmanner, samples of monolilaments (23 cm. length by 0.4-0.5 diameter)obtained from a mixture of polypropylene and polystyrene were found toexhibit tensile strengths up to 6 kg. and elongation at break Values upto The following specific embodiments exemplify but do not limit thestretching process of the present invention.

Example Tenaeity 6.2 g./ den. Elongation 15 percent. Knot strength 5g./den.

The process according to the invention is particularly suitable forpolypropylene or polypropylene mixtures having a very high intrinsicviscosity, generally higher than 1.5, more particularly of about 2-2.2.It can, however, be appliedwithout substantial variations-also to thepreparation of monotilaments obtained from polypropylene having anintrinsic viscosity lower than 1.5 e.g. of 1.3.

The polymers processed by this invention can be obtained by polymerizingpropylene or styrene with the stereospecilic catalysts of Natta et al.previously mentioned, wherein the polymerizates from such a process areless than 50% extractable with boiling n-heptane and the non-extractableportion is made up of isotactic macromolecules.

lt is understood that the inventor intends to claim, as a part of hisinvention, any variation, substitution and changes that lie within thescope of the invention and the hereinafter appended claims and intendsto include within the scope of said claims such changes as may beapparent to those skilled in the art in the practice of the principlesof this invention and within the scope as set forth in thehereinabove-stated specilication.

It will be understood that the invention is susceptible to modificationin order to adapt it to different usages and conditions, and,accordingly, it is desired to comprehend such modications within theinvention as may fall within the scope of the appended claims.

I claim:

l. A process for improving the properties of meltextruded monolamentscontaining polypropylene made up prevailingly of isotacticcrystallizable macromolecules non-extractable with boiling n-heptane,which comprises the steps of (1) quenching the polypropylene-containingmonotilament immediately after extrusion thereof, (2) subjecting thequenched monolilament to a lirst stretching stage at room temperaturewith a stretching ratio of from 3:1 to 5:1, (3) subjecting the stretchedmonolament to a second stretching stage at about C. with a stretchingratio of from 1.5 to 1.9, and (4) subjecting the twice stretchedmonofilament to a third stretching stage at room temperature with astretching ratio of from 1.1:1 to 1.2: l.

2. The process as described in claim l, wherein the monolament, in step1, is quenched to about 20 C.

3. The process as described in claim l, wherein the stretching ratio ofstep 2 is 3.8:1 and the stretching ratio of step 3 is 1.711.

4. A process as described in claim l, characterized by the additionalstep of maintaining the thrice stretched lilament from step 4 in thestretched stage for about 24 hours and then subjecting it to a steamtreatment at 100 C. for approximately 10 minutes in order to completecrystallization of the isotactic macromolecules and to obtain a higherelasticity.

5. After-stretched monotilaments of polypropylene made up prevailinglyof isotactic erystallizable macromolecules and having an intrinsicviscosity higher than 1.5, said filaments having a tenacity of 6.2g./den., a knot strength not lower than 5 g./ den., and diameters ofabout 01.307040 mm., and being substantially free of areas of neckingdown" along the length thereof.

6. After-stretched monolaments of polypropylene made up prevailingly ofisotactic crystallizable macromolecules and having an intrinsicviscosity of from about 2 to 2.2, said laments having a tenacity of 6.2g./den., a knot strength not lower than 5 g./der1., and diameters ofabout D30-0.40 mm., and being substantially free of areas of neckingdown along the length thereofl 7. A bristle comprised of anafter-stretched monolament of a mixture of polypropylene made upprevailingly of isotactic, crystallizable macromolecules and polystyrenemade up of isotactic, crystallizable macromolecules, said filamenthaving a tensile strength of about 6 kg./cm.2 and an elongation at breakvalue up to 20%.

8. The bristle of claim 7, wherein the ratio of polypropylene topolystyrene is 9:1.

References Cited in the le of this patent UNITED STATES PATENTS2,161,766 Rugeley et al. June 6, 1939 FOREIGN PATENTS 538.782 BelgiumDec. 6, 1955 1,167,990 France Aug. 25, 1958

1. A PROCESS FOR IMPROVING THE PROPERTIES OF MELTEXTRUDED MONOFILAMENTSCONTAINING POLYPROPYLENE MADE UP PREVAILINGLY OF ISOTACTICCRYSTALLIZABLE MACROMOLECULES NON-EXTRACTABLE WITH BOILING N-HEPTANE,WHICH COMPRISES THE STEPS OF (1) QUENCHING THE POLYPROPYLENE-CONTAININGMONOFILAMENT IMMEDIATELY AFTER EXTRUSION THEREOF, (2) SUBJECTING THEQUENCHED MONOFILAMENT TO A FIRST STRECHING STAGE AT ROOM TEMPERATUREWITH A STRECHING RATIO OF FROM 3:1 TIO 5:1M (3) SUBJECTING THE STRECHEDMONOFILAMENT TO A SECOND STRETCHING STAGE AT ABOUT 100*C. WITH ASTRETCHING RATIO OF FROM 1.5 TO 1.9, AND (4) SUBJECTING THE TWICESTRETCHED MONOFILAMENT TO A THIRD STRETCHING STAGE AT ROOM TEMPERATUREWITH A STRETCHING RATIO OF FROM 1.1:1 TO 1.2:1.